Ben Simmons has shrugged off taunts from rabid Boston Celtics fans and fresh barbs from rival NBA Rookie of the Year candidate Donovan Mitchell.

Simmons and his Philadelphia 76ers were soundly beaten 117-101 by the Celtics in game one of their Eastern Conference semi-final series on Monday at Boston's TD Garden arena.

Celtics fans harassed Simmons throughout the game, including chanting "not a rookie" when the Australian was shooting free throws and during other parts of the game.

"I don't care," Simmons told reporters.

"It doesn't affect me at all."

Simmons is favourite to win the Rookie of the Year Award after a record-breaking first year playing in the league, although Mitchell, Celtics fans, former NBA players and US media commentators have questioned whether he should be eligible.

The Melbourne-born 21-year-old was drafted No.1 by the 76ers in 2016 but sat out the entire 2016/17 season with a foot injury.

During his year of rehab he stayed with the team, worked with coaches and became acclimatised to the NBA, something critics believe gave Simmons an advantage over "true" rookies like the Utah Jazz's Mitchell and the Celtics' Jayson Tatum who were drafted in 2017 and played straight away.

The NBA classifies Simmons' current season his rookie season and eligible for the award.

Mitchell has trolled the Australian over the past month, including wearing a jumper with the definition of a rookie written across it, and on Monday during the Celtics-76ers game the Jazz guard took to social media to take another dig.

Mitchell also tweeted four laughing emojis at the time the TV broadcast of the game captured the chants.

Celtics chanted "he's a rookie" when Tatum stepped up for free throws against the 76ers.

Tatum played like a Rookie of the Year winner on Monday with 28 points to join the great Larry Bird as the only Celtics rookie over the past half-century to score 25 points or more in a play-off game.

He sidestepped the controversy in a post-game interview on Monday.

Simmons slams it down

"No comment," Tatum said when a reporter asked if he was a better rookie than Simmons.

"I'm just focused on winning, not really match-ups."

Simmons had 18 points, seven rebounds and six assists in the loss to the Celtics.

His game was marred by seven turnovers.

Simmons said the 76ers were "rusty" after the six-day break the team endured after quickly defeating the Miami Heat 4-1 in round one and then waiting for the Celtics to eliminate the Milwaukee Bucks in a seven-game series that ended on Saturday.

"That's the frustrating part but obviously those few days off was not the best for us," Simmons said.